This will be short, as I only have a few minutes to blog. My students seem to want their homeworks graded for some reason.

Yesterday, astronomers at UC Santa Cruz and the Carnegie Observatories announced that they had found the first known planet that may be habitable. The press release, available here, does a great job of describing the discovery, the discovery process, and what we know about the planet. Alas, many of the news stories that have popped up online and on television do a poor job of all of these, which has led to some very garbled announcements.

In short, though, the planet is about three or four times the mass of the Earth, and it orbits a red dwarf star that has at least five other planets. The star orbits within what astronomers call the "habitable zone", or a region around the star where liquid water can exist on a planet's surface.

The planet, called Gliese 581g, orbits a red dwarf star called Gliese 581. Red dwarfs have less mass then the sun and they don't shine nearly as brightly or as hotly, so this planet is ...